1. Field of the Invention
The present invention relates to process control systems including computer-based materials management. More precisely, the present invention relates to a feed forward process control system used in semiconductor fabrication based on material groupings.
2. Description of the Related Art
A semiconductor fabrication plant for manufacturing high-performance circuits such as microprocessors must produce quality, uniform integrated circuits to tight specifications and tolerances. A typical process flow in a fabrication plant includes several processing stages utilizing multiple diverse processing machines. Generally, a manufacturing facility includes several processing machines for some or all processing stages. The processing machines for a particular stage may include multiple different types, versions, generations, and models and thus have very different performance characteristics and capabilities. The processing machines often have some differences in calibration, configuration, and setup characteristics that additionally vary performance. Furthermore, each processing machine inherently has some variability in performance over time due to natural aging or degradation of components and application of scheduled maintenance.
This diversity in processing equipment results in some variability in performance that leads, in turn, to variation in the fabricated circuits that affects the electrical characteristics of the manufactured circuits, the operating speed of the fabricated parts, and the relative incidence of rework that is necessary to produce circuits that conform to specifications.
A processing "recipe" is applied at each of the several processing stages and defines processing parameters such as processing durations, dosages, intensities, and the like to achieve predefined specifications. The processing recipe is determined generally on a theoretical and experiential basis. Unfortunately, each of the several processing stages is not independent of the other stages so that variability in one stage may affect the processing characteristics, and thus modify the optimum recipe, of a subsequent stage.
However, a conventional fabrication plant does not identify the processing history of a particular wafer nor distinguish among multiple wafers in storage. A conventional fabrication plant includes storage for storing or holding wafers in various stages of manufacture. The completed stages of processing for each wafer are identified and designated, for example, on a label affixed to the wafer or affixed to a container holding multiple wafers having the same stage of fabrication. For example, in a large-scale fabrication facility, a stack of wafers is held in a temporary storage designated for awaiting photolithography processing. The stack of wafers is exposed in lithography processing and transferred to a temporary storage designated for awaiting etch processing. Therefore, although the processing stage of a wafer is continually known, specific processing characteristics of a wafer identifying the processing machine utilized at a particular processing step and the settings and calibration of the processing machine during performance of the step is not utilized. Conventional process control systems for semiconductor processing lack a capability to distinguish variations in processing parameters and characteristics for processed material samples. Conventional process control systems for semiconductor processing also lack a capability to modify processing at subsequent steps in response to variations in processing parameters and characteristics.
What is needed is a process control system and operating method for monitoring, tracking, and adjusting to the manufacturing variability of processing among different processing machines, machine sequences, and machine setups. What is needed is a process control system and operating method that track specific process parameters and characteristics throughout the processing steps applied to a material sample.